Particles flowing through openings in objects
I tried this with my work.

Blender is not good for many types of CFD, especially particle flow traces through volumes.  (Blender's particles don't have vector/pressure fields to behave correctly, but can sort of, see bottom.) 

If you need something engineering-level realistic and want a challenge, look into OpenFoam.  You can import the path traces back into blender: https://www.youtube.com/watch?v=5-GtdRLfeFI
Not animated though.  There's opportunities for better imports though, perhaps there's something better, or someone can script it for you... or perhaps just other tools like Paraview will do what you want.

Blender particles don't flow with air flow pressure, with each other smoothly around objects, etc, they're more like pellets out of a shotgun and like to bounce off/ stop suddenly on surfaces if you turn collisions on.  Not how light particles in air would behave.

There's the "fluid" type... that will get them to go with each other, but still don't slow/speed up/swirl realistically around meshes like air would.

You can make clever use of force fields and try to emulate how the particles will flow, limit the ranges and tweak a ton, add a bit of turbulence etc...
Play with simple flows first.  For what you're describing without seeing your mesh, that's what I would try.

A harder Blender option: I've got fairly close to a real looking simulation using a smoke sim, smoke flow force field driven by that smoke sim, and a particle system (volume emitter inside the smoke sim) with low mass particles, and the gravity field weight set to 0.  It works ok for very simple shapes and needs a ton of tweaking though.  It works for wide open spaces, but not when the flow opening is constricted, it slows down instead of speeding up... (see Bernoulli's principle.)  but that can be faked somewhat with more forcefields... but then you're guessing/emulating again, not simulating.